A pin grid array (PGA) socket is used for connecting an integrated circuit (IC), such as an application-specific integrated circuit (ASIC), to a circuit substrate, such as a printed circuit board (PCB). PGA sockets typically comprise a base that supports a plurality of contacts, and a cover that includes a plurality of insertion holes. The base is mounted on the circuit substrate to form an electrical connection with circuits on the circuit substrate. The cover is attached to the base prior to assembly of the circuit substrate so that the lateral surfaces of the circuit substrate, base, and cover are stacked in a parallel arrangement.
Typical PGA socket covers have rows and columns of insertion holes. The exact number of insertion holes and the orientation of the insertion holes typically depends on the types of ICs to be connected to the circuit substrate. The rows and columns of insertion holes can be spaced on interstitial centers calculated to accommodate the terminal densities of the ICs. Currently available ICs can have terminals spaced on about 0.05-inch centers or less.
Historically, when it was desired to connect an IC to a circuit substrate, the terminals of the IC were forcibly inserted into the insertion holes of the cover and against the contacts to form an electrical connection between the terminals of the IC and the electrically conductive contacts. It was found that the insertion force required to establish an adequate electrical connection is considerable and can lead to difficulty in installing and removing the IC. Moreover, the terminals of the IC can be damaged easily as a result of its installation and removal.
Therefore, low insertion force (LIF) and zero insertion force (ZIF) PGA sockets have been developed to reduce the insertion forces needed to establish an electrical connection between the contacts and the terminals. The covers of LIF or ZIF PGA sockets are typically attached to the base so that the cover is movable over the lateral surface of the base. An actuator or other mechanism for camming the cover over the surface of the base is included so that the contacts are deflected against the terminals of the IC. The base cover can have contact support walls for supporting the individual contacts.
These LIF and ZIF devices, however, also can cause the terminals of the ICs to be damaged. For example, as the cover moves over the surface of the base, the portion of the terminals extending beneath the cover can be forced against the contacts. This can create a shear force and a moment which cause the terminals to bend or to break. Additionally, the mating force between the contact and the terminal can damage the terminal since the terminals themselves are not provided with any support in the mating region.
Therefore, there is a need for a ZIF PGA socket that can be used to connect an IC to a circuit substrate without causing the portion of the terminals extending beneath the cover to be forced against the contacts, thus reducing the incidence of terminal damage. Moreover, the ZIF PGA socket should be compatible with ICs having terminals spaced on 0.05-inch centers or less.